The retina of the eye contains the cones and rods that detect colors. In the center of the retina is the macula lutea, which is about ⅓ to ½ cm in diameter. The macula provides detailed vision, particularly in the center (the fovea), because the cones are higher in density. Blood vessels, ganglion cells, inner nuclear layer and cells, and the plexiform layers are all displaced to one side (rather than resting above the cones), thereby allowing light a more direct path to the cones.
Under the retina are the choroid, comprising a collection of blood vessels embedded within a fibrous tissue, and the deeply pigmented epithelium, which overlays the choroid layer. The choroidal blood vessels provide nutrition to the retina (particularly its visual cells).
There are a variety of retinal disorders, whose current treatment is not optimal. The retina may tear, form holes and separate from the underlying choroid.
Age-related macular degeneration (AMD) is the major cause of severe visual loss in the United States for individuals over the age of 55. AMD occurs in either an atrophic or (less commonly) an exudative form. In exudative AMD, blood vessels grow from the choriocapillaris through defects in Bruch's membrane, and in some cases the underlying retinal pigment epithelium (choroidal neovascularization or angiogenesis). Organization of serous or hemorrhagic exudates escaping from these vessels results in fibrovascular scarring of the macular region with attendant degeneration of the neuroretina, detachment and tears of the retinal pigment epithelium, vitreous hemorrhage and permanent loss of central vision. This process is responsible for more than 80% of cases of significant visual loss in patients with AMD.
Several studies have recently described the use of laser photocoagulation in the treatment of initial or recurrent neovascular lesions associated with AMD (Macular Photocoagulation Study Groups (1991) in Arch. Ophthal. 109:1220; Arch. Ophthal. 109:1232; Arch Ophthal. 109:1242). Unfortunately, AMD patients with subfoveal lesions subjected to laser treatment experienced a rather precipitous reduction in visual acuity (mean 3 lines) at 3 months follow-up. Moreover, at two years post-treatment treated eyes had only marginally better visual acuity than their untreated counterparts (means of 20/320 and 20/400, respectively). Another drawback of the procedure is that vision after surgery is immediately worse.
Choroidal neovascularization (CNV) has proven recalcitrant to treatment in most cases. Laser treatment can ablate CNV and help to preserve vision in selected cases not involving the center of the retina, but this is limited to only about 10% of the cases. There is no other treatment available to correct CNV. Unfortunately, even with successful laser photocoagulation, the neovascularization recurs in about 50-70% of eyes (50% over 3 years and >60% at 5 years). (Macular Photocoagulation Study Group, Arch. Ophthalmol. 204:694-701 (1986)). In addition, many patients who develop CNV are not good candidates for laser therapy because the CNV is too large for laser treatment, or the location cannot be determined so that the physician cannot accurately aim the laser. Thus, until the present invention, there has been a long-felt need for methods that will prevent or significantly inhibit choroidal neovascularization.
In addition to AMD, choroidal neovascularization is caused by such retinal disorders as: presumed ocular histoplasmosis syndrome, myopic degeneration, angioid streaks and ocular trauma. Angiogenic damage associated with retinal and intravitreal neovascularization occurs in a wide range of disorders including diabetic retinopathy, venous occlusions, sickle cell retinopathy, retinopathy of prematurity, retinal detachment, ocular ischemia and trauma.
Citation of the above documents is not intended as an admission that any of the foregoing is pertinent prior art. All statements as to the date or representation as to the contents of these documents is based on the information available to the applicant and does not constitute any admission as to the correctness of the dates or contents of these documents.